Modeling the Hydrologic Processes of a Depressional Forested Wetland in South Carolina, U.S.A.
Depressional forested wetlands or geographically isolated wetlands such as cypress swamps and Carolina bays are common land features in the Atlantic Coastal Plain of the southeastern US. Those wetlands play important roles in providing wildlife habitats, water quality improvement, and carbon sequestration. Great stresses have been imposed on those important ecosystems due to rapid human population growth and climate change in the region. The objectives of this research were to (1) test a distributed forest hydrology model, FLATWOODS, for a Carolina bay wetland system using seven years of water table data and (2) apply the validated model to understand how wetland position (geomorphology) and geology affect lateral groundwater flow directions. The research site is a 6-ha depressional wetland known as a Carolina bay and is located in Eamberg County, South Carolina on the Lower Coastal Plain of the southeastern US (32.88 N, 81.12 W). Model calibration (1998) and validation (1997, 1999-2003) data span a wet and a long drought period allowing testing of the model for a wide range of weather conditions. While the major input to the wetland is atmospheric rainfall and output from the wetland is through evapotranspiration, modeling results suggest that the Carolina bay is a flow-through wetland, receiving discharged groundwater from one part of the upland area, but losing water as groundwater recharge to the other side, especially during wet periods in winter months. The simulation study also suggests that groundwater flow direction is controlled by the gradient of the underlying hydrologic restricting layer beneath the wetland-upland continuum, not by the topographic gradient of land surface. Groundwater flow appeared to change flow direction during the transition period during the wet-dry cycle. The changes depend on the geomorphoiogy and underlying geology of the wetland-upland continuum.